Anti-Rotation Feature for an Engine Tappet

ABSTRACT

An alignment feature for preventing in-bore rotation of an engine tappet. A first portion extends outwards from a tappet and a second portion extends into a hole in the tappet. The first portion extends longitudinally past the mounting hole such that when the feature and tappet are installed in an engine bore, the entire feature is prevented from rotation within the hole. The second portion extending orthogonally from the first portion into the mounting hole need not be close-fitting to the hole. The first portion may be substantially semi-cylindrical, having a convex cylindrical outer surface for fitting the walls of a semi-cylindrical channel in the engine bore and a concave cylindrical inner surface for fitting the outer wall of the tappet. The pin portion is preferably cylindrical. Other pin shapes are possible. The alignment feature may or may not be hardened.

RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/134,133, filed Jul. 7, 2008, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to tappets that are reciprocally slidable in bores in internal combustion engines; more particularly, to such tappets that must maintain rotational orientation in such bores during reciprocation; and most particularly, to a simple and inexpensive anti-rotation feature for attachment to a tappet during manufacture of an engine.

BACKGROUND OF THE INVENTION

Tappets are well known in the engine arts for converting rotary motion of camshaft lobes into reciprocating linear motion that is useful in driving engine combustion valves or other engine devices, for example, fuel pumps for supplying high pressure fuel rails. As used herein, the generic term “tappet” should be taken to mean any such cam-actuated linear-acting device, including but not limited to hydraulic valve lifters for both valve-in-block and valve-in-head engines, and deactivation hydraulic valve lifters for use in engines having variable valve actuation (VVA).

In modern engines, a tappet typically includes a roller for rolling along the cam lobe surface to reduce friction and wear. While a roller is a significant technological improvement, it brings with it a requirement that the tappet be prevented from rotation during reciprocation, in order to maintain proper roller orientation to the camshaft lobe surface. Further, in VVA engines, typically the deactivation mechanism is fed by one or more oil galleries in the engine, which arrangement can benefit from fixed orientation of the lifter.

Because a cylindrical engine bore is the simplest and least expensive shape for receiving a tappet, it has not proved economical to provide a non-rotation flat in an engine bore for mating with a non-rotation flat on a tappet. Rather, it is known in the prior art to prevent rotation by forming a longitudinal channel in the side of a tappet bore, and providing a mating feature such as a pin extending outwards from the side of the tappet to ride in the channel. The channel may be rectilinear or cylindrical. In the prior art, the tappet pin is hardened to Rockwell C hardness of about 58 or higher, and is press-fit into the similarly-hardened tappet body. Because the tolerances between the two hardened parts is too tight for the parts to be machined to size cost-effectively, in practice suitable matching of pin to hole is achieved by the laborious process of sorting through the manufactured tolerances of tappet holes and pin diameters.

What is needed in the art is a simple, inexpensive, anti-rotation feature for easy attachment to a roller tappet that prevents rotation of the tappet in an engine bore having an anti-rotation channel, and that does not require close fit to the hole in the tappet body.

It is a principal object of the present invention to reduce the cost of manufacture of an internal combustion engine.

SUMMARY OF THE INVENTION

Briefly described, a hardened anti-rotation feature in accordance with the present invention comprises a first portion for extending outwards from the surface of a tappet and a second or pin portion for extending into a mounting hole in the tappet. Unlike somewhat similar prior art anti-rotation features, however, the first portion of the present improved feature extends longitudinally to either or both sides of the mounting hole such that when the feature and tappet are installed in an engine bore, the entire feature is prevented from rotation within the hole. Thus, the second portion extending orthogonally from the first portion into the mounting hole need not be particularly close-fitting to the hole. In a presently preferred embodiment, the first portion is substantially semi-cylindrical, having a convex cylindrical outer surface for fitting the walls of a semi-cylindrical channel in the engine bore and a concave cylindrical inner surface for fitting the outer wall of the tappet. The pin portion is preferably cylindrical for ease of fabrication of both the pin portion and the tappet hole. Obviously, other cross-sectional shapes, such as rectangular, oval, and the like as may be desired for any particular application are fully comprehended by the present invention. The anti-rotation feature may further be hardened for improved wear resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional elevational view of a roller tappet riding on a camshaft lobe, showing a prior art anti-rotation pin extending into a longitudinal channel in an engine bore;

FIG. 2 is a cross-sectional elevational view of an embodiment in accordance with the present invention, showing an anti-rotation feature extending into the longitudinal channel shown in FIG. 1;

FIG. 3 is an isometric view of the anti-rotation feature shown in FIG. 2; and

FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 2.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a tappet 10 is slidably disposed in a bore 12 in an engine 14. Longitudinally adjacent and parallel to bore 12 is an anti-rotation channel 16 opening into bore 12. Tappet 10 is provided with a roller 18 for riding on the surface of a camshaft lobe 20 and a transverse hole 22 extending through wall 24 into a chamber 25. In accordance with the prior art, a close-fitting hardened pin 26 is press-fit into hole 22 and extends into channel 16 to prevent rotation of tappet 10 within bore 12, thus maintaining alignment of roller 18 on cam lobe 20.

The problems inherent in this prior art arrangement, which are eliminated by the present invention, are discussed above.

Referring now to FIGS. 2 through 4, an anti-rotation feature 126 in accordance with the present invention replaces prior art pin 26. Feature 126 comprises a first portion 128 for extending outwards from the surface of a tappet into channel 16, which in the presently-preferred example is cylindrical but alternatively may be non-cylindrical, such as rectangular. A second or pin portion 130 extends into hole 22 in tappet 10. First portion 128 extends longitudinally 132, 134 in channel 16 past hole 22 such that when feature 126 and tappet 10 are installed into engine bore 12, the entire feature 126 is prevented from rotation within hole 22. Thus, second portion 130 extending orthogonally from first portion 128 into hole 22 need not be particularly close-fitting to the hole, as in the prior art for pin 26. In a presently preferred embodiment, first portion 128 is substantially semi-cylindrical, having a convex cylindrical outer surface 136 for fitting the walls of channel 16 and a concave cylindrical inner surface 138 for fitting the outer wall 27 of tappet 10. Pin portion 130 is preferably cylindrical for ease of fabrication of both the pin portion and the tappet hole, and preferably is chamfered 140 to facilitate insertion. Preferably, pin portion 130 is peened to tappet 10 in chamber 25 by deforming pin portion 130, after assembly, resulting in an interference fit with hole 22. Optionally, pin portion 130 may also be welded to tappet 10.

In one embodiment, feature 126 is not hardened after forming, resulting in an as-formed material hardness of around RC25. Optionally, feature 126 may be hardened for improved wear resistance. For example, feature 126 may be through-hardened to around RC50 using known hardening processes. In another example, feature 126 may be heat treated using a ferritic nitrocarborizing (FNC) process which provides a thin hardened layer having a thickness of about 0.1 mm. When an FNC process is used to harden the feature, since only a thin hardened layer is produced, a peening process may be used to deform pin portion 130 after the feature is assembled into tappet 10.

While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims. 

1. An alignment feature for preventing rotation of an engine tappet in a bore of an internal combustion engine, comprising: a) a first portion extending outwards from said tappet for riding in a channel in said engine longitudinal of said bore; and b) a second portion extending into a mounting hole formed in said tappet, wherein said first portion extends longitudinally past said mounting hole such that when said alignment feature and said tappet are installed in said bore and said channel, said alignment feature is prevented from rotation within said mounting hole and said tappet is prevented from rotation within said bore.
 2. An alignment feature in accordance with claim 1 wherein said channel is cylindrical, and wherein an outer surface of said first portion is cylindrically convex to fit said channel.
 3. An alignment feature in accordance with claim 2 wherein an inner surface of said first portion is cylindrically concave to fit an outer surface of said tappet.
 4. An alignment feature in accordance with claim 1 wherein said mounting bore and said second portion are cylindrical.
 5. An alignment feature in accordance with claim 1 wherein said tappet is selected from the group consisting of hydraulic valve lifter, deactivation hydraulic valve lifter, and fuel pump lifter.
 6. An alignment feature in accordance with claim 1 wherein said mounting bore extends through a wall of said tappet into a chamber therein.
 7. An alignment feature in accordance with claim 6 wherein said second portion extends into said chamber.
 8. An alignment feature in accordance with claim 7 wherein said second portion is captured in said second chamber.
 9. An alignment feature in accordance with claim 8 wherein a method for said capture is selected from the group consisting of spot welding and peening of said second portion to said tappet.
 10. An alignment feature in accordance with claim 1 wherein at least said first portion is hardened above a Rockwell C hardness of about
 25. 11. An alignment feature in accordance with claim 1 wherein said alignment feature in its entirety is hardened above a Rockwell C hardness of about
 25. 12. An alignment feature in accordance with claim 11 wherein said second portion is captured in said second chamber by peening to define an interference fit between said second portion and said mounting hole.
 13. An internal combustion engine comprising an alignment feature for preventing rotation of an engine tappet in an engine bore, said alignment feature including, a first portion extending outwards from said tappet for riding in a channel in said engine longitudinal of said bore, and a second portion extending into a mounting hole formed in said tappet, wherein said first portion extends longitudinally past said mounting hole such that when said alignment feature and said tappet are installed in said bore and said channel, said alignment feature is prevented from rotation within said mounting hole and said tappet is prevented from rotation within said bore. 